1. Field of the Invention
The present invention relates to a high-pressure water electrolysis apparatus which electrically decomposes water to generate oxygen at an anode and to generate hydrogen under a pressure higher than the pressure of the oxygen at a cathode.
2. Description of the Related Art
Hydrogen gases are used as fuel gases for generating electricity with fuel cells. Generally, water electrolysis apparatus are used to generate hydrogen gases. A water electrolysis apparatus incorporates a solid polymer electrolyte membrane for electrically decomposing water to generate hydrogen (and oxygen). Electrode catalyst layers are disposed on the respective sides of the solid polymer electrolyte membrane, making up a membrane electrode assembly. Current collectors are disposed on the respective opposite sides of the membrane electrode assembly, making up a unit.
A plurality of such units are stacked, and a voltage is applied across the stack while water is supplied to the current collectors on the anode side. On the anodes of the membrane electrode assemblies, the water is decomposed to produce hydrogen ions (protons). The hydrogen ions move through the solid polymer electrolyte membranes to the cathodes, where the hydrogen ions combine with electrons to generate hydrogen. On the anodes, oxygen generated together with hydrogen is discharged with excess water from the units.
A high-pressure water electrolysis apparatus is occasionally employed to generate hydrogen at a cathode under a pressure (e.g., several tens MPa) higher than the pressure of oxygen generated at an anode. For example, such a high-pressure hydrogen producing apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2006-070322. As shown in FIG. 11 of the accompanying drawings, the disclosed high-pressure hydrogen producing apparatus includes a solid polymer membrane 1, a cathode current collector 2a and an anode current collector 2b which are disposed on respective both sides of the solid polymer membrane 1 so as to face each other, separators 3a, 3b stacked respectively on the cathode current collector 2a and the anode current collector 2b, and fluid channels 4a, 4b defined respectively in the separators 3a, 3b to expose portions of the cathode current collector 2a and the anode current collector 2b. 
The solid polymer membrane 1, the cathode current collector 2a and the anode current collector 2b, and the separators 3a, 3b are sandwiched between end plates 6a, 6b with insulating members 5a, 5b stacked on the separators 3a, 3b and interposed between the separators 3a, 3b and the end plates 6a, 6b. 
The fluid channels 4a defined in the separator 3a on the cathode side house therein titanium disc springs 7 which normally bias the cathode current collector 2a toward the solid polymer membrane 1. A perforated plate 8 of titanium is interposed between the disc springs 7 and the solid polymer membrane 1. Therefore, the contact resistance between the solid polymer membrane 1 and the cathode current collector 2a does not increase even when a high pressure is developed on the cathode side.
On the cathode side where high-pressure hydrogen is generated, there are stacked the disc springs 7, the perforated plate 8, and the cathode current collector 2a which are separate members.
While the high-pressure hydrogen producing apparatus is in operation, electrons flow successively through the separator 3a, the disc springs 7, the perforated plate 8, and the cathode current collector 2a, a reaction is caused to generate hydrogen on the surface of the catalyst of the solid polymer membrane 1.
The disc springs 7, which provide electrically-conductive paths, have small areas of contact with the separator 3a and the perforated plate 8. The surfaces of the disc springs 7 that are held in contact with the separator 3a and the disc springs 7 are liable to change easily, e.g., tend to have their contact resistance easily affected by oxidization. In addition, the disc springs 7 are likely to be deteriorated easily by electric currents flowing therethrough.